1. Field of the Invention
The present invention relates to an Ethernet Passive Optical Access Network (EPON) system, and more particularly to an apparatus and method for allocating a bandwidth for up-stream data transmission to a plurality of Optical Network Units (ONUs) in the EPON system in which the plurality of ONUs are connected to a single Optical Line Terminal (OLT).
2. Description of the Related Art
Typically, an Access Network (AN) is indicative of a communication area positioned between a service provider (e.g., Central Office (CO), a Head-End, or a Point-of-Presence (POP), etc.) and a service subscriber capable of receiving a specific service from the service provider.
Presently, a variety of networks are widely used as the aforementioned Access Network (AN), for example, currently xDSL networks (e.g., an Asymmetric Digital Subscriber Line (ADSL), and a Very high-data rate Digital Subscriber Line (VDSL)) based on a telephone line via which low-speed data and voice-oriented data are processed, and a Hybrid Fiber Coaxial (HFC) network serving as an optical/coaxial hybrid network, etc.
However, as technologies of a high-speed Internet, a high-speed LAN (Local Area Network), and a home network have recently been developed, and a variety of applications (e.g., a voice data service and a multimedia streaming service, etc.) required for the aforementioned technologies have been rapidly developed, an amount of a bandwidth required for an Access Network (AN) is rapidly increased, and the xDSL network based on a telephone line and the HFC network based on a coaxial cable cannot satisfy the aforementioned rapidly-increasing AN bandwidth requirement.
With the increasing development of a variety of communication services such as VOD-, CATV-, and HDTV-services, such that many developers have recently conducted intensive research into the implementation of high-speed Internet traffic and an Access Network (AN) which uses an optical line in a Broadband Convergence Network (BCN) environment. Specifically, a Passive Optical Network (PON) system has long been considered to be the most appropriate alternative network for an FTTx (Fiber To The x) scheme in technical-, economical-, and evolutional-aspects of communication networks.
Although the PON system and associated technologies have been initially developed for an Asynchronous Transfer Mode (ATM) network, the ATM PON (APON) based on ATM technologies has not been widely used by users due to a variety of problems (i.e., system complexity, high costs, Ethernet-based subscriber traffic increase, and difficulty of video service accommodation, etc.). Recently, the EPON (Ethernet PON) standardization based on the IEEE 802.3ah EFM (Ethernet in the First Mile) task force has been completed. The EPON technology transmits an Ethernet frame to a destination without modifying a protocol of the Ethernet frame in a passive optical line arranged between a subscriber and a Central Office (CO), such that it is more cost-effective than conventional networks based on telephone- and coaxial-lines. As a result, many developers have recently conducted intensive research into the aforementioned EPON technology, and a variety of companies have currently manufactured chips capable of satisfying a prescribed EPON standard. Recently, a variety of Access Networks (ANs) based on the EPON system have rapidly come into widespread use.
FIG. 1 is a block diagram illustrating a structure for transmitting up-stream data and down-stream data in a conventional Ethernet EPON system, and its operation principles.
Referring to FIG. 1, a conventional EPON system includes an Optical Line Terminal (OLT) 100, a splitter 105, and a plurality of Optical Network Units (ONUs) 110, 120, and 130. The EPON system includes a PTM (Point-To-Multipoint) structure in which the ONUs 110, 120, and 130 share the OLT 100 via a single optical fiber. In other words, a down-stream transmission scheme for transmitting data from the OLT 100 to the ONUs 110, 120, and 130 is implemented with a broadcast scheme. On the contrary, an up-stream transmission scheme for transmitting data from the ONUs 110, 120, and 130 to the OLT 100 is implemented with a MTP (Multipoint-To-Point) scheme.
The OLT 100 is located at the CO (Central Office). The ONUs 110, 120, and 130 collect subscriber traffic generated from a plurality of subscriber terminals (also called user terminals) 140˜145. The splitter 150 connects the single OLT 100 to the plurality of ONUs 110, 120, and 130 according to a specific ratio of 1:N, such that an optical distribution network between the OLT 100 and the ONUs 110, 120, and 130 is formed. Down-stream traffic 160 configured in the form of broadcast data is transmitted to a destination in the EPON system, such that it is similar to conventional Ethernet traffic. However, the up-stream transmission is implemented when the ONUs 110, 120, and 130 simultaneously transmit the up-stream traffic 150 to the single OLT 100. For example, the OLU 110 for use in the EPON system shares network resources with other ONUs 120 and 130 to transmit up-stream traffic L1, and the OLT 100 controls access authority of the shared network resources of the ONUs 110, 120, and 130. Therefore, a method for evenly and effectively allocating a bandwidth and a Multi Point Control Protocol (MPCP) are employed, such that they prevent an unexpected data collision from being generated when a tree-structure EPON system transmits up-stream data, and an effective bandwidth allocation process is executed. The easiest method from among a plurality of up-stream data transmission methods is a fixed bandwidth allocation scheme capable of dividing a bandwidth into sub-bandwidths according to the number of the registered ONUs 110, 120, and 130, and allocating the sub-banwidths to the ONUs 110, 120, and 130, respectively.
However, the fixed bandwidth allocation scheme has difficulty in supporting Quality of Service (QoS), and cannot provide individual ONUs 110, 120, and 130 with different bandwidths instead of the same bandwidths although there is a spare bandwidth in an overall bandwidth. A variety of dynamic bandwidth allocation methods have been proposed to obviate the aforementioned problems of the fixed bandwidth allocation scheme. A representative method from among the dynamic bandwidth allocation methods is an Interleaved Polling with Adaptive Cycle Time (IPACT) method. The IPACT method enables the OLT 100 to transmit a gate message to the next ONU 120 according to down-stream transmission before a current ONU 110 having transmission authority performs the last transmission. In more detail, if individual ONUs 110, 120, and 130 performs up-stream data transmission according to the gate message of the OLT 100, they inform the OLT 100 of buffer information of the ONUs 110, 120, and 130, such that the dynamic bandwidth allocation process can be performed. However, although the IPACT method provides different bandwidths according to the buffer information of the ONUs 110, 120, and 130, it can distinguish individual traffic requirement characteristics from each other on the condition that a variety of traffics having different characteristics are mixed, such that it has difficulty in providing an appropriate QoS.